<varlistentry> <term><option>--verbose</option> / <option>-v</option></term> <listitem> <para> Increases the level of verbosity of diagnostic messages printed on standard error. For each Nix operation, the information printed on standard output is well-defined; any diagnostic information is printed on standard error, never on standard output. </para> <para> This option may be specified repeatedly. Currently, the following verbosity levels exist: </para> <variablelist> <varlistentry> <term>0</term> <listitem> <para> <quote>Errors only</quote>: only print messages explaining why the Nix invocation failed. </para> </listitem> </varlistentry> <varlistentry> <term>1</term> <listitem> <para> <quote>Informational</quote>: print <emphasis>useful</emphasis> messages about what Nix is doing. </para> </listitem> </varlistentry> <varlistentry> <term>2</term> <listitem> <para> <quote>Talkative</quote>: print more informational messages. </para> </listitem> </varlistentry> <varlistentry> <term>3</term> <listitem> <para> <quote>Chatty</quote>: print even more informational messages. </para> </listitem> </varlistentry> <varlistentry> <term>4</term> <listitem> <para> <quote>Debug</quote>: print debug information: </para> </listitem> </varlistentry> <varlistentry> <term>5</term> <listitem> <para> <quote>Vomit</quote>: print vast amounts of debug information. </para> </listitem> </varlistentry> </variablelist> </listitem> </varlistentry> <varlistentry> <term><option>--build-output</option> / <option>-B</option></term> <listitem> <para> Causes the output written by build actions to standard output and standard error to be echoed to standard error, regardless of verbosity level. By default, it is only echoed at a verbosity level of at least 4 (<quote>Debug</quote>), and is suppressed at lower levels. Note that it is always written to a log file in <filename><replaceable>prefix</replaceable>/nix/var/log/nix</filename>. </para> </listitem> </varlistentry>